Today we call it “plagiarism,” but back in the heyday of baroque music, in the late 17th to early 18th centuries, reworking another composer’s music — or your own — was considered an indication of respect. Bach did it copiously from, for instance, the music of Telemann, Vivaldi, Lutheran hymn melodies and — most of all — himself. On Sunday at the National Presbyterian Church, under the auspices of the Washington Bach Consort, organist/harpsichordists J. Reilly Lewis (the WBC’s music director) and Scott Dettra (the Washington National Cathedral’s organist) collaborated on a beautifully conceived program that focused on Bach’s music for organ (the “Choral Preludes”) and for harpsichord, with roots in numerous sources.

Chorales based on Lutheran hymns or folk melodies, sung here by a quartet of WBC singers, were followed by organ preludes on the same melodies. A concerto for two harpsichords began life as a piece either for two violins or for violin and oboe (the chronology being uncertain), and there were several pieces that Bach lifted and reworked from Telemann and a number of lesser composers of the time. What gave the program such coherence was the grouping of works that shared a common spirit (exuberance, reflection, hope and the like) and a common tonality. A quintet of strings was the “orchestra” for the harpsichord concertos.

That Lewis and Dettra, who split the organ and harpsichord assignments equally, had quite different approaches to how Bach’s music moves, only added to the program’s riches. Dettra’s was the more Germanic. His playing had a rhythmic momentum that gave his performances a sense of inevitability and drive. Lewis, leaning toward a Gallic idiom, moved the music more elastically with hints of rubato. Together on two of Bach’s Double Concertos, they compromised with a Germanic reading of the Concerto in C Minor, BWV 1060, and a more Frenchified version of the Concerto in C, BWV 1061. Both went well. The vocal quartet handled their assignments with professional aplomb and, except for the tentative delivery of an instrumental “Sinfonia,” the strings offered fine support.

The afternoon’s real problem was the church’s acoustics. Lewis told the audience that he thought it was a wonderful space for music. Maybe he was speaking as an organist because, in fact, the church’s fine Aeolian-Skinner sounds terrific there. But the sounds of the harpsichords and strings were reduced to a muffled fuzz, as if the performance took place behind some sort of sonic scrim.

Reinthaler is a freelance writer.